1. Field of the Invention
The present invention relates to a process for determining traffic conditions using stationary data collection devices, e.g., detectors, that are installed at installation sites along a road network. The data collection devices collect data concerning traffic conditions at the respective installation sites in keeping with an established measurement procedure and then, in keeping with an established reporting procedure, transmit information derived from this data to a traffic center for further analysis.
2. Background of Related Art
European patent publication 0 029 201 B1 discloses an interactive dynamic route guidance system in which specially equipped vehicles engage in two-way communication with a traffic computer. In this system, beacons equipped with an infrared transmitter/receiver device are installed at important junctions in the road network. Vehicles with a corresponding transmitter/receiver device receive from a traffic computer current information, as for example the shortest route, with respect to time, to a desired target or destination. The main sources of information for the traffic computer are "float-along" sampling vehicles, which move along with the flow of traffic. The sampling vehicles transmit information, as for example, the time between important junctions and the waiting or delay times at stoplights, to the traffic computer. The traffic computer, based on this information, provides route guidance and traffic direction, for example, traffic guidance information may be transmitted to a vehicle and output via a control device on a display in the vehicle.
Another system for determining traffic conditions with detectors installed in a stationary manner is disclosed in U.S. Pat. No. 5,317,311. The detectors and associated sensor system, which is located, for example, on overpasses above the lanes of a highway, measure the average speed of passing vehicles and determine the number of vehicles that pass in a given unit of time. This data is transmitted through a data transmission channel such as a telephone line to a traffic center. In this system, the average speeds reported by the detectors are transmitted by transmitting devices from the traffic center to vehicles equipped with receiving devices. The data is received by the vehicles and graphically displayed on a display as a map of the sites of particular detectors. Drivers use this information to detect and avoid current problem areas in the road network or system. The detectors measure the average speeds so as to continuously monitor the traffic.
In contrast to the method of ascertaining traffic conditions disclosed in European patent publication 0 029 201 in which the relevant traffic data is detected by sampling vehicles and forwarded to data collection stations, e.g., beacons, which, in turn, transmit all of the data to a traffic center; the system disclosed in U.S. Pat. No. 5,317,311 collects the data using stationary sensor systems installed in the detectors themselves and transmits or reports only a limited amount of the data collected or detected by the detectors to the traffic center. In particular, data is transmitted or reported to the traffic center only when the average speed of the passing vehicles detected by the detectors during a certain time period falls below a preestablished threshold value, as for example a threshold value of approximately 50 km/h. As a result, the burden and bandwidth of the communication channel for data transmission is substantially reduced. This reduction in data transmission, however, disadvantageously limits the use of the system to situations in which there is very heavy traffic, e.g., traffic jams or similar situations. Thus, this traffic detection system is not suitable for detecting conditions in which the traffic is moderate or the roads are completely empty because of the limited reporting or transmission of collected data. The detection of conditions in which there is moderate traffic or in which the roads are completely empty is only possible if all of the information or data is reported which would require a corresponding increase in communications expenditure between the detectors and the traffic center.
The object of the present invention is therefore to provide a process for determining traffic conditions which establishes relatively inexpensive communications between the stationary detectors and the traffic center and is not limited in the information being observed or for use in only particular types of traffic conditions.